Simple Addon 50 lines - Crash blender - what I do bad?
Is it as simple as it could be?.
A TL;DR comment turned into answer:
Doesn't crash for me... but does throw errors. Some of the issues as I see them.
Sure it's a simple little addon, but.. appears to be some added and IMO unnecessary complexity added too. (bling).
Is there really any need to type hint the usual suspects  and  familiar arguments of  self, context ?
def execute( self : bpy.types.Operator , context : bpy.types.Context )

Let's look at  Text Editor &gt; Templates &gt; Python &gt; Operator Simple and make a small change
def execute(self, context):
    print(type(self))
    main(context)
    return {'FINISHED'}

output
&lt;class '__main__.SimpleOperator'&gt;
&lt;bpy_struct, Object(&quot;Armature&quot;) at 0x7f1e0c715008&gt;

ie the operator type is not an instance of  bpy.types.Operator
Any need to toggle the active object?
There is no need to toggle the active object with
context.view_layer.objects.active = None
context.view_layer.objects.active = obj

and  since context is an argument of method there is never any need to see bpy.context
Dynamic Paint Modifier.
Once a dynamic paint modifier is added to an object, it cannot be added again.  If you try and do so again it will not add a modifier and return None. (NoneType) is not an instance of bpy.types.DynamicPaintModifier
Main thread.
Any benefit in using if not __package__ vs if __name__ == &quot;__main__&quot; ?  Will it always equate?